Candidate and Training Environment: I am seeking a K01 Mentored Career Development Award to obtain additional training, which will facilitate my transition into an independent scientist. My long-term research goal is to understand how manipulation of T cell receptor signals can be used to alter or prevent diverse T cell functions, i the interest of developing therapeutic strategies for T cell mediated diseases. As a PhD student under the mentorship of Dr. Deborah Fowell, I determined the requirements for the tyrosine kinase Itk in CD4+ T cell differentiation. During the course of those studies, I gained training in cellular T cell immunology, mostly related to the isolation, activation, differentiation, and effecor cytokine production of primary mouse CD4+ T cells. My postdoctoral training in the laboratory of Dr. Arthur Weiss has so far focused on developing and characterizing a unique experimental inhibitor for the tyrosine kinase ZAP-70. We showed that this inhibitor system is highly specific, titratable, and can rapidly and reversibly inhibit ZAP-70 kinase activity, making this system a very useful tool for modulating the magnitude of T cell receptor signaling. At this point of my postdoctoral training, the technology and techniques that I have learned to use are well suited to understand how manipulations of T cell receptor signaling can be applied to alter T cell function, which could be important for developing novel therapeutic strategies for T cell mediated autoimmune diseases, such as rheumatoid arthritis. Further training in the analysis autoimmune disease models, and the signals that drive the activation and differentiation of autoreactive T cells will allow me to develop an independent research plan and transition into an independent scientist. The proposed studies will take place under the mentorship of Dr. Arthur Weiss at the University of California, San Francisco (UCSF). Dr. Weiss is a rheumatologist, a renowned expert in the field of T cell signal transduction, and a distinguished mentor as the recipient of te UCSF Lifetime Achievement in Mentoring award. Additionally, I will be able to get advice from my collaborators/consultants at UCSF, Dr. Abul Abbas and Dr. Mark Anderson, who have considerable experience and expertise in the fields of autoimmunity and tolerance. The Department of Microbiology and Immunology at UCSF is also highly regarded and is a rich environment for gaining additional training and input for studies of autoimmunity. Research: T cell responses are associated with multiple autoimmune diseases such as rheumatoid arthritis (RA). Therefore, a therapeutic strategy for blocking T cell function could be useful for treatment of RA and other T cell-mediated autoimmune diseases. While inhibiting all T cell function would block the autoreactive T cell response, a more desirable strategy would selectively block the subset of T cells responsible for causing pathology. Previous work and preliminary data suggest that inhibition of the tyrosine kinase ZAP-70 could fit these criteria. First, the activation of conventional CD4+ and CD8+, but not regulatory T cells, requires ZAP-70 catalytic activity. Secondly, preliminary data indicates that CD4+ T cells undergoing Th17 differentiation are substantially more sensitive to ZAP-70 inhibition as compared to Th1 and Th2 differentiating cells. Together these data suggest that ZAP-70 inhibition could be very useful for treating autoimmune diseases mediated by autoreactive Th17 responses, such as RA. In Aim 1 of this proposal, I aim to determine how Th17 differentiating cells are differentially sensitive to ZAP-70 inhibition. First, I will test the hypothesis that Th17 cells are preferentially derived from cellsthat express relatively low levels of ZAP-70. Secondly, I plan to take advantage of the increased sensitivity of Th17 cells to ZAP-70 inhibition to identify TCR signaling pathways that are most sensitive to ZAP-70 inhibition and thus highly important for Th17 differentiation. Aim 2 will determine whether incomplete or transient inhibition of ZAP-70 results in subsequent T cell hyporesponsiveness and identify potential mechanisms that drive this process. Lastly, the goal of Aim 3 is to determine the efficacy of ZAP-70 inhibition as a therapy to either prevent or ameliorate pathology associated with collagen-induced arthritis, and experimental autoimmune encephalomyelitis, two mouse models of Th17-mediated autoimmune disease. I anticipate that these studies will show for the first time that ZAP-70 inhibition effectively inhibits T cell-associated pathology in settings of autoimmunity. Ultimately, these studies may provide new insights into how T cell receptor signaling can alter the differentiation and effector functions ofT cells, which will be important for developing novel therapies for T cell-mediated autoimmune disease.